When exporting arcs to dxf from Rhino sometimes the lines are open in autocad. Now granted these openings are <.00001 inch in distance, and the vertexes are in the same location. Autocad will join them as a closed curve, but when you are zoomed in they appear open. This might be a visual problem and the problem is somewhere else, however, the machine that this is going to produces erroneous cuts at these points.
one thing that seems to fix this is to export using the ‘SaveSmall’ setting on.
The machine does not produce errors with this setting on. It’s possible the actual fix is from another source but I wanted to see if there are any known issues with exporting open lines and the ‘SaveSmall’ option.